The U.S. Coast Guard is warning beachgoers to “remain clear” if they come across a silver-shaped cylinder along the shoreline, as it could be an armed flare.

Coast Guard Sector Lake Michigan said in a statement three phosphorus pyrotechnic flares were unaccounted for after a joint military exercise with the Coast Guard and Air Force earlier this month offshore Milwaukee.

Coast Guard Sector Lake Michigan issued a warning for three missing phosphorus pyrotechnic flares. (Ninth Coast Guard District)

However, three phosphorus pyrotechnics are still unaccounted for.

The missing pyrotechnics are still considered armed when they do not activate.

A satellite image of Lake Michigan. Several armed flares are missing after a Coast Guard exercise and beachgoers are being urged to be careful. (Google Earth)

Phosphorus pyrotechnics produce a red smoke and flame that can reach temperatures of 2,900 degrees Fahrenheit, according to military officials.